The present invention relates to a cationic resin composition, more specifically to a cationic resin composition capable of forming a cured coating film which is excellent in both corrosion resistance and an aptitude for the cationic electrodepositable coating of a rust preventive steel plate.
A cationic resin composition is used mainly as a cationic electrodepositable coating composition for wide-ranged uses including an undercoating composition for car bodies, and those having various characteristics have so far been developed. Proposed as a conventional cationic resin composition is, for example, a coating composition having excellent corrosion resistance and improved in an electrodepositable coating aptitude and an adhesive property toward a rust preventive steel plate, in which used as a vehicle component is a modified epoxy resin obtained by internally plasticizing an epoxy resin having an amino group and/or a quaternary ammonium salt group as a hydrophilic group with a plasticizer such as polyamide, polyester and polyether and blended is a rust preventive pigment, for example, a lead compound or a chromium compound such as lead chromate, basic lead silicate and strontium chromate. In recent years, however, hazardous compounds such as lead compounds and chromium compounds are restricted in use thereof from a viewpoint of pollution problems, and techniques which can improve a corrosion resistance of the coating film without blending such hazardous compounds are expected to be developed.
On the other hand, an epoxy resin which is internally plasticized with a plasticizer such as polyamide, polyester and polyether tends to reduce a corrosion resistance of the coating film, and therefore it is considered to use an epoxy resin containing no plasticizing modifier to thereby elevate the corrosion resistance. However, this provides the problem that the electrodepositable coating aptitude against a rust preventive steel plate is reduced. In order to solve such problems, it is proposed that added as a plasticizer for an epoxy resin are, for example, polyol resins such as polyesterpolyols, polyetherpolyols, polyurethanepolyols and acrylpolyols; and polymers including polyolefins such as polybutadiene and polyethylene. Involved therein, however, is the problem that these materials not only do not have a sufficiently high compatibility with epoxy resins and are not effective so much for elevating a rust preventive steel plate aptitude but also reduce a corrosion resistance of the coating film by adding in a large amount.
A main object of the present invention is to provide a cationic resin composition useful in particular as a cationic electrodepositable coating, comprising an epoxy resin as a base material and capable of forming a coating film which is excellent both in a corrosion resistance and a rust preventive steel plate aptitude without using hazardous compounds such as lead compounds and chromium compounds.
Intensive researches repeated by the present inventors have resulted in finding that the object described above can be achieved by combining, as a vehicle component in a cationic resin composition, a certain kind of amino group-containing epoxy resin with a specific polyol-modified amino group-containing epoxy resin and a blocked polyisocyanate curing agent.
Thus, the present invention provides a cationic resin composition comprising the following components:
(A) an amino group-containing epoxy resin which is prepared by adding an amino group-containing compound (a-2) to an epoxy resin (a-1) having an epoxy equivalent of 400 to 3000,
(B) a polyol-modified amino group-containing epoxy resin which is prepared by making an epoxy resin (b-1) having an epoxy equivalent of 180 to 2500 react with an amino group-containing compound (b-2) and with a polyol compound (b-3) obtained by adding caprolactone to a compound having plural active hydrogen groups, and
(C) a blocked polyisocyanate curing agent, component (A) being 40 to 70% by weight, component (B) being 4 to 40% by weight, and component (C) being 10 to 40% by weight, based on the total solid contents of (A), (B) and (C).
The cationic resin composition of the present invention shall be explained below in further details.
Amino group-containing epoxy resin which is used as component (A) in the cationic resin composition of the present invention is prepared by adding an amino group-containing compound (a-2) to an epoxy resin (a-1). Said epoxy resin (a-1) can have an epoxy equivalent falling in a range of 400 to 3000, preferably 450 to 2500, and more desirably 500 to 2200. Further, it has suitably a number average molecular weight falling in a range of usually 500 to 5000, particularly 600 to 4500, and more particularly 800 to 4000. An epoxy resin obtained by the reaction of a polyphenol compound with epihalohydrin, for example epichlorohydrin, is particularly suited as an epoxy resin (a-1) from the viewpoint of corrosion resistance of coating film.
Polyphenol compounds which can be used for producing the above epoxy resin include, for example, bis(4-hydroxyphenyl)-2,2-propane (bisphenol A), 4,4-dihydroxybenzophenone, bis(4-hydroxyphenyl)methane (bisphenol F), bis(4-hydroxyphenyl)-1,1 -ethane, bis(4-hydroxyphenyl)-1,1-isobutane, bis(4-hydroxy-tert-butyl-phenyl)-2,2-propane, bis(2-hydroxynaphthyl)methane, tetra(4-hydroxyphenyl)-1,1,2,2-ethane, 4,4-dihydroxy-diphenylsulfone (bisphenol S), phenol novolak and cresol novolak.
Particularly suited as an epoxy resin obtained by the reaction of a polyphenol compound with epichlorohydrin is a compound which is derived from bisphenol A, and which is represented by the following formula: 
wherein n is 1 to 10.
Commercially available products of such epoxy resin include, for example, products which are marketed from Japan Epoxy Resin Co., Ltd. in the trade names of Epikote 828EL, ditto 1002, ditto 1004 and ditto 1007.
For the amino group-containing compound (a-2) as a cationic property-providing component with which to introduce an amino group into the above-mentioned epoxy resin (a-1) and to thereby cationize said epoxy resin, there are suitably used amine compounds having at least one active hydrogen which performs an addition reaction with an epoxy group of epoxy resin (a-1), for instance amine compounds which have at least one primary or secondary amino group in molecule. Concrete examples of such compounds include mono- or di-alkylamines such as monomethylamine, dimethylamine, monoethylamine, diethylamine, monoisopropylamine, diisopropylamine, triisopropylamine, monobutylamine and dibutylamine; alkanolamines such as monoethanolamine, diethanolamine, mono(2-hydroxypropyl)amine, di(2-hydroxypropyl)amine, tri(2-hydroxypropyl)amine, monomethylaminoethanol and monoethylaminoethanol; alkylenepolyamines such as ethylenediamine, propylenediamine, butylenediamine, hexamethylenediamine, tetraethylenepentamine, pentaethylenehexamine, diethylaminopropylamine, diethyelenetriamine and triethylenetetramine, and ketimine-reduced compounds of these polyamines; alkyleneimines such as ethyleneimine and propyleneimine; and cyclic amines such as piperazine, morpholine and pyrazine.
The above-mentioned addition reaction between epoxy resin (a-1) and amino group-containing compound (a-2) may be conducted by a known method. For instance, epoxy resin (a-1) and amino group-containing compound (a-2) are allowed to react with each other in an organic solvent like hydrocarbon type solvent such as heptane, toluene, xylene, octane and mineral spirits; ester type solvent such as ethyl acetate, n-butyl acetate, isobutyl acetate, ethyleneglycol monomethylether acetate and ethyleneglycol monobutylether acetate; ketone type solvent such as methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone and cyclohexane; alcohols such as methanol, ethanol, iso-propanol, n-butanol, sec-butanol and isobutanol; and ether type solvent such as n-butylether, dioxane, ethyleneglycol monomethylether and ethyleneglycol monoethylether, at a temperature of about 80 to about 130xc2x0 C. The proportion of epoxy resin (a-1) to amino group-containing compound (a-2) used in the addition reaction is not strictly restricted, but can suitably be changed according to the species of starting materials used and special properties which products are desired to have. Usually, however, the weight ratio of (a-1)/(a-2) is preferably within a range of 90/10 to 60/40, in particular 85/15 to 70/30.
Thus obtained amino group-containing epoxy resin (A) can have an amine value within a range of 30 to 100, preferably 40 to 80.
Polyol-modified amino group-containing epoxy resin which is used as component (B) in the cationic resin composition of the present invention is prepared by making an epoxy resin (b-1) react with an amino group-containing compound (b-2) and with a polyol compound (b-3) obtained by adding caprolactone to a compound having plural active hydrogen groups. The above-mentioned epoxy resin (b-1) can have an epoxy equivalent within a range of 180 to 2500, preferably 200 to 2000, much desirably 400 to 1500, and suitably has a number average molecular weight within a range of at least 200, in particular 400 to 4000, especially 800 to 2000.
Like the above-mentioned epoxy resin, also epoxy resin (b-1) is preferably obtained by a reaction between a polyphenol compound and epichlorohydrin, and, thus, may be appropriately chosen from those which are recited above with respect to epoxy resin (a-1).
For amino group-containing compound (b-2) which is used for the purpose of introducing amino group, as a cationizable group, into the above-mentioned epoxy resin (b-1), there may also be employed those which are recited above as amino group-containing compound (a-2) with which to introduce amino group into epoxy resin (a-1).
In the present invention, furthermore, a polyol compound (b-3) is made to react for the purpose of internally plasticizing (modifying) the epoxy resin (b-1). For this polyol compound (b-3), there are employed those which are produced by adding caprolactone to a compound (hereinafter referred to as xe2x80x9cactive hydrogen-compoundxe2x80x9d) having plural active hydrogen groups.
An active hydrogen group means an atomic group containing at least one active hydrogen and includes, for example, an alcoholic hydroxyl group, a primary amino group and a secondary amino group. The compound having plural groups of such active hydrogen group in a molecule, i.e., active hydrogen-compound, includes, for example:
(i) low molecular weight polyols,
(ii) linear or branched polyetherpolyols,
(iii) linear or branched polyesterpolyols,
(iv) amine compounds having a primary amino group and/or a secondary amino group or hydroxylamine compounds having a primary amino group and/or a secondary amino group in combination with a hydroxyl group.
These active hydrogen group-containing compounds can have a number average molecular weight falling in a range of usually 62 to 5,000, preferably 62 to 4,000 and more preferably 62 to 1,500. The active hydrogen-compound is suitably a compound having at least two groups and less than 30 groups, particularly 2 to 10 groups of the active hydrogen groups per molecule on the average.
The low molecular weight polyol (i) described above is a compound having at least two alcoholic hydroxyl groups in a molecule, and to be specific, it includes, for example, diols such as ethylene glycol, propylene glycol, 1,3-butylene glycol 1,4-butanediol, 1,6-hexanediol, diethylene glycol, dipropylene glycol, cyclohexane-1,4-dimethylol, neopentyl glycol, triethylene glycol and hydrogenated bisphenol A; triols such as glycerin, trimethylolethane and trimethylolpropane; tetrols such as pentaerythritol and xcex1-methylglycoside; hexols such as sorbitol and dipentaerythritol; and octols such as sucrose.
The linear or branched polyetherpolyol (ii) described above can have a number average molecular weight falling in a range of usually 62 to 10,000, preferably 62 to 2,000, and to be specific, it includes, for example, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, poly(ethylenexe2x80xa2propylene) glycol, bisphenol A ethylene glycol ether and bisphenol A propylene glycol ether which are produced by ring-opening reaction of alkylene oxides (e. g., ethylene oxide, propylene oxide, butylene oxide and tetrahydrofuran).
The linear or branched polyesterpolyol (iii) described above can have a number average molecular weight falling in a range of usually 200 to 10,000, preferably 200 to 3,000, and to be specific, it includes, for example, compounds obtained by polycondensation reaction of organic dicarboxylic acids or anhydrides thereof with organic diols on the condition of organic diol excess. The organic dicarboxylic acid used in this case includes aliphatic, alicyclic or aromatic organic dicarboxylic acids having 2 to 44 carbon atoms, particularly 4 to 36 carbon atoms, for example, succinic acid, adipic acid, azelaic acid, sebacic acid, maleic acid, fumaric acid, glutaric acid, hexachloroheptane-dicarboxylic acid, cyclohexanedicarboxylic acid, o-phthalic acid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid and tetrachlorophthalic acid. Further, in addition to these carboxylic acids, capable of being used in combination in small amounts are anhydrides of polycarboxylic acids having 3 or more carboxyl groups and adducts of unsaturated fatty acids.
The organic diol component includes, for example, alkylene glycols such as ethylene glycol, propylene glycol, butylene glycol, 1,4-butanediol, 1,6-hexanediol, and neopentyl glycol, and dimethylolcyclohexane. They may be used, if necessary, in combination with a small amount of polyol such as trimethylolpropane, glycerin and pentaerythritol.
The preceding amine compound having a primary amino group and/or a secondary amino group or amine compound (iv) having a primary amino group and/or a secondary amino group in combination with a hydroxyl group includes, for example, alkylamines such as butylenediamine, hexamethylenediamine, tetraethylene-pentamine and pentaethylenehexamine; alkanolamines such as monoethanolamine, diethanolamine, triethanolamine, mono(2-hydroxypropyl)amine and di(2-hydroxypropyl)amine; alicyclic polyamines such as 1,3-bisaminomethyl-cyclohexane and isophoronediamine; aromatic polyamines such as xylylenediamine, metaxylenediamine, diaminodiphenylmethane and phenylenediamine; alkylenepolyamines such as ethylenediamine, propylenediamine, diethylene-triamine and triethylenetetramine; and other amine compounds such as polyamides and polyamideamines which are derived from piperizine and these polyamines, amine adducts with epoxy compounds, ketimines and aldimines.
Among the compounds having plural active hydrogen groups described above, suited are the compounds of (i), (ii), (iii) and (iv), particularly compounds selected from the group consisting of ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, hydrogenated bisphenol A, glycerin, trimethylolethane, trimethylolpropane, pentaerythritol dipentaecrythritol, polyethylene glycol polypropylene glycol, polytetramethylene glycol, poly(ethylenexe2x80xa2propylene) glycol, bisphenol A ethylene glycol ether, bisphenol A propylene glycol ether, butylenediamine, hexamethylenediamine, monoethanolamine, diethanolamine, triethanol-amine, isophoronediamine, ethylenediamine, propylene-diamine, diethylene-triamine and triethylenetetramine.
On the other hand, caprolactone which can be added to these active hydrogen-compounds include xcex3-caprolactone, xcex5-caprolactone and xcex4-caprolactone, among which xcex5-caprolactone is particularly suited.
The addition reaction between the above active hydrogen-compounds and caprolactone can be carried out by conventionally known methods. To be specific, it can be carried out, for example, by heating an active hydrogen-compound and caprolactone at a temperature of about 100 to about 250xc2x0 C. for about one to about 15 hours in the presence of a catalyst including titanium compounds such as tetrabutoxytitanium and tetrapropoxytitanium, organic tin compounds such as tin octylate, dibutyltin oxide and dibutyltin laurate, and metal compounds such as stannous chloride.
In general, the catalyst described above can be used in an amount of 0.5 to 1,000 ppm based on the total amount of active hydrogen-compound and caprolactone. Caprolactone can be used in an amount falling in a range of usually 1 to 30 moles, preferably 1 to 20 moles and more desirably 1 to 15 moles per equivalent of active hydrogen group (that is, per active hydrogen) of active hydrogen-compound.
The polyol compound (b-3) thus obtained has together a high plasticizing performance based on the active hydrogen-compound, a high compatibility with an epoxy resin based on (poly)caprolactone and a high reactivity attributable to a terminal hydroxyl group, and therefore is very useful as an internal plasticizer for an epoxy resin for a coating composition.
The polyol compound (b-3) can contain caprolactone-originated units in a proportion falling in a range of usually 20 to 95% by weight, preferably 25 to 90% by weight, and can have a number average molecular weight falling in a range of usually 300 to 10,000, preferably 400 to 5,000.
The polyol-modified amino group-containing epoxy resin used as component (B) in the resin composition of the present invention can be produced by subjecting the epoxy resin (b-1) described above, by a known method, to an addition reaction with the amino group-containing compound (b-2) and the polyol compound (b-3) having a terminal hydroxyl group originating in caprolactone. The reaction of the polyol compound (b-3) and the amino group-containing compound (b-2) with the epoxy resin (b-1) can be carried out in an optional order. In general, however, the polyol compound (b-3) and the amino group-containing compound (b-2) are suitably made to react with the epoxy resin (b-1) at the same time. A single terminal of the polyol compound (b-2) is preferably added to the skeleton of the epoxy resin (b-1).
The above-mentioned addition reaction can be carried out usually in a suitable solvent at a temperature of about 90 to about 170xc2x0 C., preferably about 100 to about 150xc2x0 C. for one to 5 hours, preferably 2 to 4 hours. Said solvent includes, for example, hydrocarbons such as toluene, xylene and n-hexane; esters such as methyl acetate, ethyl acetate and butyl acetate; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and methyl amyl ketone; amides such as dimethylformamide and dimethylacetamide; alcohols such as methanol, ethanol n-propanol and iso-propanol; and mixtures thereof.
The proportion of reaction components in the addition reaction described above is not strictly restricted, and can suitably be changed according to uses of the resin composition. The ratio of epoxy resin (b-1), the amino group-containing compound (b-2) and the polyol compound (b-3) falls suitably in the following ranges based on the total solid matter weight of the three components described above:
Epoxy resin (b-1):
Usually 60 to 90% by weight, preferably 62 to 85% by weight and more desirably 62 to 80% by weight
Amino group-containing compound (b-2):
Usually 5 to 25% by weight, preferably 6 to 19% by weight and more preferably 6 to 18% by weight
Polyol compound (b-3):
Usually 5 to 30% by weight, preferably 5 to 20% by weight and more preferably 5 to 18% by weight
The blocked polyisocyanate curing agent which is used as component (C) in the cationic resin composition of the present invention is an addition reaction product of a polyisocyanate compound with an isocyanate blocking agent in almost stoichiometric amounts. The polyisocyanate compound used includes, for example, aromatic, aliphatic or alicyclic polyisocyanate compounds such as tolylenediisocyanate, xylilenediisocyanate, phenylenediisocyanate, bis(isocyanatemethyl)cyclohexane, tetramethylenediisocyanate, hexamethylenediisocyanate, methylenediisocyanate and isophoronediisocyanate, and terminal isocyanate group-containing compounds obtained by reacting excess amounts of these polyisocyanate compounds with low molecular active hydrogen-containing compounds such as ethylene glycol, propylene glycol, trimethylolpropane, hexanetriol and castor oil.
On the other hand, the isocyanate blocking agents described above are added to, and block, isocyanate groups of the polyisocyanate compounds, and the blocked polyisocyanate compounds formed by the addition are stable at a room temperature. However, when they are heated at a baking temperature (usually, about 100 to about 200xc2x0 C.) of the coating film, the blocking agent is preferably dissociated to regenerate free isocyanate groups. Examples of blocking agent satisfying such requisite include lactam compounds such as xcex5-caprolactam and xcex3-butyrolactam; oxime compounds such as methyl ethyl ketoxime and cyclohexanoneoxime; phenol compounds such as phenol, p-t-butylphenol and cresol; aliphatic alcohols such as n-butanol and 2-ethylhexanol; aromatic alkylalcohols such as phenylcarbinol and methylphenylcarbinol; and ether alcohol base compounds such as ethylene glycol monobutyl ether.
The cationic resin composition provided by the present invention comprises amino group-containing epoxy resin (A), polyolmodified amino group-containing epoxy resin (B) and blocked polyisocyanate curing agent (C) as mentioned above.
The proportion of the above-mentioned components (A), (B) and (C) in the resin composition of the present invention is as follows, based on the total solid matter weight of these components:
Component (A): 40 to 70% by weight, preferably 43 to 67% by weight, more desirably 45 to 65% by weight;
Component (B): 5 to 40% by weight, preferably 7 to 37% by weight, more desirably 8 to 35% by weight;
Component (C): 10 to 40% by weight, preferably 15 to 40% by weight, more desirably 17 to 35% by weight.
The cationic resin composition of the present invention can be prepared, for example, by sufficiently mixing amino group-containing epoxy resin (A), polyol-modified amino group-containing epoxy resin (B) and blocked polyisocyanate curing agent (C), and then neutralizing the resultant mixture, usually in an aqueous medium, with acidic neutralizer such as formic acid, acetic acid, lactic acid, propionic acid, citric acid, malic acid and sulfamic acid by which to reduce the above-mentioned components water-soluble or water-dispersible. Thus, there are obtained a resin composition suitable as an emulsion for cationic electrodepositable coating.
As a neutralizer, acetic acid, formic acid or a mixture thereof is particularly suited, and the use of these acids elevates a finishing property, a throwing property and a low temperature-curing property of the coating composition formed as well as the stability of paint.
When used as a coating composition, the resin composition of the present invention may contain a bismuth compound as a rust preventive. The kind of the bismuth compound to be blended is not specifically restricted, and includes, for example, inorganic bismuth compounds such as bismuth oxide, bismuth hydroxide, basic bismuth carbonate, bismuth nitrate and bismuth silicate. Among them, bismuth hydroxide is particularly preferred.
Also usable as the above-mentioned bismuth compound are organic acid bismuth salts which are produced by a reaction between two or more organic acids and a bismuth compounds described above, and in which at least one of said organic acids is aliphatic hydroxycarboxylic acid. The organic acids which can be used for producing the above organic acid bismuth salts include, for example, glycolic acid, glyceric acid, lactic acid, dimethylolpropionic acid, dimethylolbutyric acid, dimethylolvaleric acid, tartaric acid, malic acid, hydroxymalonic acid, dihydroxysuccinic acid, trihydroxysuccinic acid, methylmalonic acid, benzoic acid and citric acid.
The inorganic bismuth compounds and the organic acid bismuth salts described above each can be used alone or may be used in combination of two or more kinds thereof.
The content of these bismuth compounds in the resin composition of the present invention is not strictly restricted, and can be changed over a wide range according to performances required of the resin composition. Usually, it falls suitably in a range of 0.01 to 10% by weight, preferably 0.05 to 5% by weight based on the resinous solid contents in the resin composition of the present invention.
Further, the cationic resin composition of the present invention can contain, if necessary, a tin compound as a curing catalyst. Said tin compound includes, for example, organic tin compounds such as dibutyltin oxide and dioctyltin oxide; and aliphatic or aromatic carboxylic acid salts of dialkyltin such as dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin diacetate, dioctyltin benzoateoxy, dibutyltin benzoateoxy, dioctyltin dibenzoate and dibutyltin dibenzoate. Among them, dialkyltin aromatic carboxylic acid salts are suitable from a viewpoint of a low temperature curability.
The content of these tin compounds in the resin composition of the present invention is not strictly restricted, and can be changed over a wide range according to performances required of the resin composition. Usually, the tin content falls suitably in a range of 0.01 to 8 parts by weight, preferably 0.05 to 5 parts by weight per 100 parts by weight of the resinous solid contents in the coating composition.
Further, if necessary, the cationic resin composition of the present invention can contain, blended therein, coating material additives such as a color pigment, an extender pigment, a rust preventive pigment, an organic solvent, a pigment dispersant and a surface-controlling agent.
The cationic resin composition of the present invention can be applied on the surface of desired substrate by cationically electrodepositable coating, In general, electrodepositable coating can be carried out on the condition of a loaded voltage of 100 to 400 V in an electrodeposition bath which is controlled usually to a bath temperature of about 15 to about 35xc2x0 C., and which comprises the coating composition of the present invention diluted with deionized water so that the solid matter concentration becomes about 5 to about 40% by weight, preferably 15 to 25% by weight, and controlled to a pH falling in a range of 5.5 to 9.
A film thickness of an electrodeposited coating film which is formed using the resin composition of the present invention is not specifically restricted, and falls preferably in a range of usually 10 to 40 xcexcm, particularly 15 to 35 xcexcm in terms of a cured coating film. A baking temperature of the coating film is suitably a temperature falling in a range of usually about 120 to about 200xc2x0 C., preferably about 140 to about 180xc2x0 C. on the surface of substrate, and the baking time is 5 to 60 minutes, preferably 10 to 30 minutes.
The cationic resin composition of the present invention is suitably used as a cationically electrodepositable coating composition, which use is however not restrictive. The cationic resin composition of the present invention can also be used as a solvent type coating material for a corrosion resistant primer of a steel plate for coating by a method such as electrostatic coating and roll coating.
Further, the resin composition of the present invention can be used as a two-liquid type room temperature-drying coating composition or as an adhesive using, as a cross-linking agent, a polyisocyanate compound and a melamine resin in place of blocked polyisocyanate curing agent.
The cationic resin composition of the present invention forms a cured coating film which is excellent in corrosion resistance, an electrodepositable coating aptitude against a corrosion-resistant steel plate and an adhesive property to a base material, and is useful as an undercoating material for car bodies, car parts and construction and building fields.